Abstract: An inductive heating device for uniformly heating a workpiece at rest has a plurality of heating coil units disposed so as to surround the workpiece. The heating coil units are connected in parallel to a power source, and a transformer is used to vary the voltage across the terminals of the outermost units to increase the current flowing through these outermost units. The device, therefore, has a very short insufficient heating temperature zone attributable to an end magnetic flux effect.

Abstract: A method for reducing the radial temperature gradient of a radiant energy emitting heated body is described. The method comprises insulating such heated body with a refractory insulating material containing an efficient absorber of the radiant energy emitted by said heated body. Specifically, materials containing trivalent dysprosium are disclosed as suitable thermal insulation for use where the heated body is at a temperature in the 1800.degree. C.-2500.degree. C. range. Also described is a crystal growth chamber for pulling unicrystalline compositions from a melt utilizing the Czochralski technique. The chamber is characterized by the placement of a refractory insulating material containing an efficient absorber of near infrared radiation around a crucible which contains the melt. Dysprosium is specifically disclosed as an efficient absorber of the near infrared radiation which is emitted by melt and crucible at the elevated temperatures employed for boule formation utilizing the Czochralski technique.

Abstract: A device is provided for melting by direct induction substances which are dielectric when cold and whose temperatures of inductibility and melting are close to each other, such as glasses or vitreous enamels. This melting is carried out inside a receptacle whose sidewall comprises a multi-turn inductor made from metal tubing whose inward-looking faces are exposed and which combines the functions of heating the charge by induction and cooling the periphery thereof. Such a receptacle which is at the same time a heating inductor and a cooling surface is applicable more especially to industrial electric furnaces for the production of molten glass or enamel by direct induction.

Abstract: An inductive heating device for heating a workpiece made of carbon has a heating coil disposed so as to surround the carbon workpiece. A first and second heat insulating layer is interposed between the workpiece and the heating coil, with the first layer being made of a carbon powder and the second layer being made of a carbon and silica powder mixture. A high frequency electrical source is used to drive the heating coil, which causes an eddy current to be induced in the workpiece, thus heating the workpiece. The first and second heat insulating layers prevent the surface of the workpiece from oxidizing and minimize heat loss from the workpiece during the heating thereof.

Abstract: A high frequency induction furnace (10) for reflowing a portion of a lightguide preform (44) in order to draw a fiber (52) therefrom. The furnace (10) has a centrally located tubular susceptor (34) therein having a thin coating of the preform material (e.g., silica) on at least a portion of the inside surface thereof. A cylinder (62) is positioned in concentric, spaced relation about the susceptor (34) and is surrounded by an insulating grain (36). A high frequency coil (38) is energized to couple its electromagnetic field to the susceptor (34) to heat and reflow a portion of the preform (44) in order to draw the fiber (52) therefrom. The thin coating prevents contaminating particulates from migrating from small cracks in the inside surface of the susceptor (34) onto the preform (44) while the cylinder (62) prevents small particulate emanating from the insulating grain (36) from being drawn through larger cracks in the susceptor and onto the preform and/or the fiber 52.

Abstract: An induction crucible furnace includes a housing having a bottom wall and side walls which define a furnace cage. A prefabricated refractory crucible made of a mixture of a dry ramming material, a sintering agent and a cold-curing binder is disposed within the furnace cage with a clearance which is filled with a non-sintering granular material sealed within the furnace with a patching compound. A plurality of induction coils are disposed within the furnace cage and are separated from a layer of the non-sintering granular material by a heat-protective layer. In a method of manufacturing of the induction crucible furnace a refractory crucible is placed onto a bed of a non-sintering granular material disposed on the bottom wall of the furnace housing.